Set errno on response when syscall actually fails

This prevents setting stale errno on responses.

Also fixes TestDiscardsUDPPacketsWithMcastSourceAddressV6 to use correct
multicast addresses in test.

Fixes #3793

PiperOrigin-RevId: 329391155

2 files changed, 46 insertions, 16 deletions

diff --git a/test/packetimpact/dut/posix_server.cc b/test/packetimpact/dut/posix_server.cc
index 0f8e279f8..de5b4be93 100644
--- a/test/packetimpact/dut/posix_server.cc
+++ b/test/packetimpact/dut/posix_server.cc
@@ -116,7 +116,9 @@ class PosixImpl final : public posix_server::Posix::Service {
     socklen_t addrlen = sizeof(addr);
     response->set_fd(accept(request->sockfd(),
                             reinterpret_cast<sockaddr *>(&addr), &addrlen));
-    response->set_errno_(errno);
+    if (response->fd() < 0) {
+      response->set_errno_(errno);
+    }
     return sockaddr_to_proto(addr, addrlen, response->mutable_addr());
   }
 
@@ -137,7 +139,9 @@ class PosixImpl final : public posix_server::Posix::Service {
 
     response->set_ret(
         bind(request->sockfd(), reinterpret_cast<sockaddr *>(&addr), addr_len));
-    response->set_errno_(errno);
+    if (response->ret() < 0) {
+      response->set_errno_(errno);
+    }
     return ::grpc::Status::OK;
   }
 
@@ -145,7 +149,9 @@ class PosixImpl final : public posix_server::Posix::Service {
                        const ::posix_server::CloseRequest *request,
                        ::posix_server::CloseResponse *response) override {
     response->set_ret(close(request->fd()));
-    response->set_errno_(errno);
+    if (response->ret() < 0) {
+      response->set_errno_(errno);
+    }
     return ::grpc::Status::OK;
   }
 
@@ -165,7 +171,9 @@ class PosixImpl final : public posix_server::Posix::Service {
 
     response->set_ret(connect(request->sockfd(),
                               reinterpret_cast<sockaddr *>(&addr), addr_len));
-    response->set_errno_(errno);
+    if (response->ret() < 0) {
+      response->set_errno_(errno);
+    }
     return ::grpc::Status::OK;
   }
 
@@ -173,7 +181,9 @@ class PosixImpl final : public posix_server::Posix::Service {
                        const ::posix_server::FcntlRequest *request,
                        ::posix_server::FcntlResponse *response) override {
     response->set_ret(::fcntl(request->fd(), request->cmd(), request->arg()));
-    response->set_errno_(errno);
+    if (response->ret() < 0) {
+      response->set_errno_(errno);
+    }
     return ::grpc::Status::OK;
   }
 
@@ -185,7 +195,9 @@ class PosixImpl final : public posix_server::Posix::Service {
     socklen_t addrlen = sizeof(addr);
     response->set_ret(getsockname(
         request->sockfd(), reinterpret_cast<sockaddr *>(&addr), &addrlen));
-    response->set_errno_(errno);
+    if (response->ret() < 0) {
+      response->set_errno_(errno);
+    }
     return sockaddr_to_proto(addr, addrlen, response->mutable_addr());
   }
 
@@ -227,7 +239,9 @@ class PosixImpl final : public posix_server::Posix::Service {
         return ::grpc::Status(grpc::StatusCode::INVALID_ARGUMENT,
                               "Unknown SockOpt Type");
     }
-    response->set_errno_(errno);
+    if (response->ret() < 0) {
+      response->set_errno_(errno);
+    }
     return ::grpc::Status::OK;
   }
 
@@ -235,7 +249,9 @@ class PosixImpl final : public posix_server::Posix::Service {
                         const ::posix_server::ListenRequest *request,
                         ::posix_server::ListenResponse *response) override {
     response->set_ret(listen(request->sockfd(), request->backlog()));
-    response->set_errno_(errno);
+    if (response->ret() < 0) {
+      response->set_errno_(errno);
+    }
     return ::grpc::Status::OK;
   }
 
@@ -244,7 +260,9 @@ class PosixImpl final : public posix_server::Posix::Service {
                       ::posix_server::SendResponse *response) override {
     response->set_ret(::send(request->sockfd(), request->buf().data(),
                              request->buf().size(), request->flags()));
-    response->set_errno_(errno);
+    if (response->ret() < 0) {
+      response->set_errno_(errno);
+    }
     return ::grpc::Status::OK;
   }
 
@@ -265,7 +283,9 @@ class PosixImpl final : public posix_server::Posix::Service {
     response->set_ret(::sendto(request->sockfd(), request->buf().data(),
                                request->buf().size(), request->flags(),
                                reinterpret_cast<sockaddr *>(&addr), addr_len));
-    response->set_errno_(errno);
+    if (response->ret() < 0) {
+      response->set_errno_(errno);
+    }
     return ::grpc::Status::OK;
   }
 
@@ -299,7 +319,9 @@ class PosixImpl final : public posix_server::Posix::Service {
         return ::grpc::Status(grpc::StatusCode::INVALID_ARGUMENT,
                               "Unknown SockOpt Type");
     }
-    response->set_errno_(errno);
+    if (response->ret() < 0) {
+      response->set_errno_(errno);
+    }
     return ::grpc::Status::OK;
   }
 
@@ -308,14 +330,18 @@ class PosixImpl final : public posix_server::Posix::Service {
                         ::posix_server::SocketResponse *response) override {
     response->set_fd(
         socket(request->domain(), request->type(), request->protocol()));
-    response->set_errno_(errno);
+    if (response->fd() < 0) {
+      response->set_errno_(errno);
+    }
     return ::grpc::Status::OK;
   }
 
   ::grpc::Status Shutdown(grpc_impl::ServerContext *context,
                           const ::posix_server::ShutdownRequest *request,
                           ::posix_server::ShutdownResponse *response) override {
-    response->set_errno_(shutdown(request->fd(), request->how()));
+    if (shutdown(request->fd(), request->how()) < 0) {
+      response->set_errno_(errno);
+    }
     return ::grpc::Status::OK;
   }
 
@@ -328,7 +354,9 @@ class PosixImpl final : public posix_server::Posix::Service {
     if (response->ret() >= 0) {
       response->set_buf(buf.data(), response->ret());
     }
-    response->set_errno_(errno);
+    if (response->ret() < 0) {
+      response->set_errno_(errno);
+    }
     return ::grpc::Status::OK;
   }
 };
diff --git a/test/packetimpact/tests/udp_discard_mcast_source_addr_test.go b/test/packetimpact/tests/udp_discard_mcast_source_addr_test.go
index d30177e64..3d2791a6e 100644
--- a/test/packetimpact/tests/udp_discard_mcast_source_addr_test.go
+++ b/test/packetimpact/tests/udp_discard_mcast_source_addr_test.go
@@ -53,6 +53,7 @@ func TestDiscardsUDPPacketsWithMcastSourceAddressV4(t *testing.T) {
 				t,
 				testbench.IPv4{SrcAddr: testbench.Address(tcpip.Address(mcastAddr.To4()))},
 				testbench.UDP{},
+				&testbench.Payload{Bytes: []byte("test payload")},
 			)
 
 			ret, payload, errno := dut.RecvWithErrno(context.Background(), t, remoteFD, 100, 0)
@@ -76,14 +77,15 @@ func TestDiscardsUDPPacketsWithMcastSourceAddressV6(t *testing.T) {
 		net.IPv6interfacelocalallnodes,
 		net.IPv6linklocalallnodes,
 		net.IPv6linklocalallrouters,
-		net.ParseIP("fe01::42"),
-		net.ParseIP("fe02::4242"),
+		net.ParseIP("ff01::42"),
+		net.ParseIP("ff02::4242"),
 	} {
 		t.Run(fmt.Sprintf("srcaddr=%s", mcastAddr), func(t *testing.T) {
 			conn.SendIPv6(
 				t,
 				testbench.IPv6{SrcAddr: testbench.Address(tcpip.Address(mcastAddr.To16()))},
 				testbench.UDP{},
+				&testbench.Payload{Bytes: []byte("test payload")},
 			)
 			ret, payload, errno := dut.RecvWithErrno(context.Background(), t, remoteFD, 100, 0)
 			if errno != syscall.EAGAIN || errno != syscall.EWOULDBLOCK {